Methods for diagnosis of cancer at an early stage are essential for cancer prevention and therapy. Many types of cancers grow from epithelial tissues, which cover inner and outer surfaces of the human body. Many of these, for example cancer in gastrointestinal tract, progress through the stage of dysplasia. Dysplasia can be defined as neoplastic tissue which is not malignant yet, but is considered to be a precursor of malignancy. If diagnosed at this stage, most tumors are curable. In the case of gastrointestinal tumors, current methods of diagnosis are based on endoscopy. However, dysplastic tissue is frequently not endoscopically apparent. Thus, detection of dysplasia in the gastrointestinal tract and other sites often relies on sporadic sampling for this "invisible" malignant precursor. However, sporadic biopsies have a high probability of missing dysplastic changes. In some cases the biopsy procedure is impossible.
Efforts toward a substitution for standard biopsies have been made in order to provide accurate diagnosis of cancerous tissue in different organs in vivo and in real time. For this purpose, optical techniques that are non-invasive do not require tissue removal and can be performed in-vivo. Such methods provide information at the microscopic level and can thus provide for the search for very small sites which are likely to be missed by standard biopsies. While most human organs can be diagnosed by means of optical techniques, they are particularly applicable to the tissues in human body lumens, since they are easily accessible by optical probes, which can be inserted into one of the channels of a conventional endoscopic tube.